Various other types of folding wheelchairs are known and one typical raising-type wheelchair, in which the upwardly raising movement of the patient is assisted by mechanism in the wheelchair itself is described in referenced U.S. Pat. No. 4,076,304. Two essentially parallel side frames have wheels attached thereto. In use, four or more foldable spreader braces hold the side frames spread apart, with a seat of flexible material therebetween. The seat may be made of fabric, leather, or the like. For storage, transport, for example in an automobile, or the like, the spreader braces can be folded or unlocked in order to move the side frames of the chair next to each other. Levers and rods are used to fold the various spreader braces together or, respectively, to lock them in extended position.
The structure works well; it does, however, have a disadvantage in that the multiplicity of spreader braces, levers and rods and the like increases the overall weight of the raising chair. Additionally, it is very difficult for an invalid to fold the wheelchair together using only his own efforts or strength; such folding, however, is frequently desirable in order to fit the wheelchair in the usual space behind the driver seat of an automobile. The relative folded space of a wheelchair makes it difficult to fit such a wheelchair in an ordinary autombile so that, frequently, special seating arrangements or requirements for placement of the wheelchair behind the driver seat may have to be met.
When erected, the wheelchair is stiff. If the wheelchair is to be used over surfaces which are not essentially flat, for example over unpaved surfaces, for sporting events or even on poorly maintained sidewalks, the substantial stiffness of the operating frame may interfere with proper engagement of all the wheels of the wheelchair with the ground surface. The chair, then, will have a tendency to be slightly tippy, which, particularly to an invalid, may be disconcerting.